Fluid catalytic cracking (“FCC”) is one of the most important conversion processes used in petroleum refineries. It is widely used to convert the high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases, and other products. However, in addition to these more desirable products, the process also yields a bottom product oil, referred to as a slurry oil (or main column bottoms (“MCB”)). Due to the nature of conventional catalytic cracking units, there is generally a significant amount of particulate matter (e.g, catalyst fine particulates) entrained in the slurry oil, along with a high-boiling, high-molecular weight hydrocarbon fraction and to a lesser degree, a portion of lower-boiling hydrocarbons.
In conventional refinery processes, a portion of the MCB is often recycled back into the main fractionation column above the entry of hot reaction product vapors, so as to cool and partially condense the reaction product vapors as they enter the main fractionation column. The remainder of the MCB is conventionally pumped out of the main fractionation column and sent to a MCB filtration unit or a tank where the fines are allowed to settle. However, conventional MCB processing methods and apparatus face significant reliability challenges due to coke accumulation and fouling that occurs at elevated temperatures.
In efforts to reduce coke accumulation and fouling, conventional MCB processing methods and systems typically involve reducing the temperature of MCB in the main fractionation column by recycling a cooled portion of the MCB as a quench liquid back into the pooled MCB in the main fractionation column. However, that separation of lighter hydrocarbons such as light cycle oil and heavy cycle oil from MCB is limited by the design and operation of conventional systems and methods. Specifically, quenching pooled MCB results in delivery of a quenched MCB stream to a separation zone at a temperature that is sub-optimal for separation.
Accordingly, it is desirable to provide methods and systems that allow for recovery of hydrocarbons from a FCC slurry stream at an elevated temperature while still quenching the majority of pooled MCB in the main fractionation column so as to provide a second FCC slurry stream at a second, reduced, temperature to reduce fouling. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and appended claims, taken in conjunction with the accompanying drawings and this background of the invention.